1. Field of the Invention
The present invention relates to a perovskite-oxide lamination, a piezoelectric device having the perovskite-oxide lamination, and a liquid discharge device using the piezoelectric device.
2. Description of the Related Art
Perovskite-type oxides are currently used in piezoelectric devices, switch devices, and the like since perovskite-type oxides exhibit ferroelectricity. For example, lead titanate zirconate (PZT) is known as a perovskite-type oxide exhibiting satisfactory piezoelectric characteristics. PZT is a ferroelectric material having spontaneous polarization even when no electric field is applied to PZT, and is reported to exhibit high piezoelectric performance at and near the morphotropic phase boundary (MPB).
However, currently, demands for higher piezoelectric performance and demands for lead-free piezoelectric materials (in consideration of the environmental load of the lead-containing materials) are increasing, and therefore development of new lead-free perovskite-oxide materials are proceeding.
In the process of the development of lead-free perovskite-type oxide materials, some perovskite-type oxides which are theoretically considered to exhibit high piezoelectric performance are known to be incapable of being formed to have a perovskite crystal structure by high-temperature baking at normal pressure, but to be capable of being formed to have a perovskite crystal structure by baking at high pressure exceeding several GPa (gigapascal). However, baking at high pressure requires complicated equipment and an uneasy process.
Some attempts to form, at normal pressure, a thin film of a material to have a perovskite crystal structure have been reported, although the material is unable to be formed to have a perovskite crystal structure unless being baked at high pressure.
M. Okada et al. (in “Synthesis of Bi(FexAl1-x)O3 Thin Films by Pulsed Laser Deposition and Its Structural Characterization”, Japanese Journal of Applied Physics, Vol. 43, No. 9B, pp. 6609-6612, 2004) report that a thin film having a perovskite crystal structure can be formed by producing a solid solution of BiAlO3 in BiFeO3, where BiAlO3 is unable to be formed to have a perovskite crystal structure unless being baked at high pressure although BiFeO3 can be easily formed to have a perovskite crystal structure. However, in this case, the thin film formed as above has properties of a solid solution, and it is impossible to realize the characteristics unique to BiAlO3.
In addition, S. Yasui et al. (in “Formation of BiFeO3—BiScO3 Thin Films and Their Electrical Properties”, Japanese Journal of Applied Physics, Vol. 45, No. 9B, pp. 7321-7324, 2006) report that a thin film having a perovskite crystal structure can be formed by producing a solid solution of BiScO3 in BiFeO3, where BiScO3 is unable to be formed to have a perovskite crystal structure unless being baked at high pressure.
Japanese Unexamined Patent Publication No. 6(1994)-239696 (hereinafter referred to as JP6-239696A) discloses a process for realizing a perovskite crystal structure by utilizing the stress produced by lattice matching with an underlying layer, as a technique for forming a thin film having a perovskite crystal structure without solid solution. Specifically, JP6-239696A discloses that a perovskite crystal structure can be realized by epitaxial growth of a high-temperature superconductivity thin film having an infinite-layer structure (which have been able to be formed only by the high-pressure synthesis) on an underlying layer of a perovskite-type oxide having the composition expressed as A2BO4, where a thin-film deposition technique such as sputtering or evaporation is used for formation of the high-temperature superconductivity thin film.
Nevertheless, the perovskite-type oxide disclosed in JP6-239696A has the composition expressed as A2BO4, and JP6-239696A does not teach the general applicability of the disclosed technique to the simple perovskite crystal structure. In addition, since the stress caused by the lattice matching with the underlying layer is relaxed in the case where the thickness of the thin film exceeds a predetermined value, there is a possibility that the thin film can become unable to be formed to have a perovskite crystal structure when the film thickness increases. That is, the thickness of the thin film which can be formed to have a perovskite crystal structure is limited.